1. Business System Development
CSC581

2. Lecture 12 Structuring System Logical Requirements

3. Summary of the previous lecture
In previous lecture, we :
Balanced high-level and low-level DFDs.
Explained differences between current physical, current logical, new physical, and new logical DFDs.
Used DFDs for analyzing information systems.
Explained use cases and use case diagrams.

4. Outlines We today’s lecture we will:
Use structured English as a tool for representing steps in logical processes in data flow diagrams.
Use decision tables and decision trees to represent logical choice in conditional statements.
Select among structured English, decision tables, and decision trees

6. Logic Modeling
Data flow diagrams do not show the logic inside the processes.
Logic modeling involves representing internal structure and functionality of processes depicted on a DFD.
Logic modeling can also be used to show when processes on a DFD occur.

7. Logic Modeling Deliverables and Outcomes
Structured English
Decision Tables
Decision Trees
State-transition diagrams
Sequence diagrams
Activity diagrams

8. Modeling Logic with Structured English
Modified form of English used to specify the logic of information processes
Uses a subset of English
Action verbs
Noun phrases
No adjectives or adverbs
No specific standards

10. Structured English is used here to describe input and output.

11. Structured English is used here to describe arithmetic operations.

12. Structured English is used here to describe repetition.

13. Structured English is used here to describe decisions.

14. Structured English is used here to describe invoking other processes.

15. Modeling Logic with Decision Tables
A matrix representation of the logic of a decision
Specifies the possible conditions and the resulting actions
Best used for complicated decision logic

16. 3 Parts of a Decision Table
Condition stubs
Lists condition relevant to decision
Action stubs
Actions that result from a given set of conditions
Rules
Specify which actions are to be followed for a given set of conditions
Indifferent Condition
Condition whose value does not affect which action is taken for two or more rules

17. Procedure for Creating Decision Tables
Name the condition and values each condition can assume
Name all possible actions that can occur
List all rules
Define the actions for each rule
Simplify the table

18. Decision Table
Note: for salaried employees the action stub chosen will always be the same…therefore hours worked is an indifferent condition

19. Reduced Decision Table
Because of indifferent condition, the complete decision table can be reduced to one with fewer rules

20. Modeling Logic with Decision Trees
A graphical representation of a decision situation
Decision situation points are connected together by arcs and terminate in ovals
Main components
Decision points represented by nodes
Actions represented by ovals
Particular choices from a decision point represented by arcs

21. Modeling Logic with Decision Trees (cont.)
Read from left to right
Each node corresponds to a numbered choice on a legend
All possible actions are listed on the far right

22. Decision tree representation of salary decision

23. Alternative decision tree representation of salary decision

24. Deciding Among Structured English, Decision Tables, and Decision Trees
Criteria
Structured English
Decision Tables
Decision Trees
Determining Conditions and Actions
Second Best
Third Best
Best
Transforming Conditions and Actions into Sequence
Checking Consistency and Completeness

25. Deciding Between Decision Tables and Decision Trees
Criteria
Decision Tables
Decision Trees
Portraying complex logic
Best
Worst
Portraying simple rules
Making decisions
More compact
Easier to manipulate

26. Summary of today’s lecture
In this lecture. we:
Used structured English as a tool for representing steps in logical processes in data flow diagrams.
Used decision tables and decision trees to represent logical choice in conditional statements.
Selected among structured English, decision tables, and decision trees.

27. Overview of the next lecture
In next lecture, we will:
Define key data modeling terms.
Draw entity-relationship (E-R) and class diagrams to represent common business situations.
Explain the role of conceptual data modeling in IS analysis and design.
Distinguish between unary, binary, and ternary relationships.
Define four types of business rules.
Compare the capabilities of class diagrams vs. E-R diagrams.
Relate data modeling to process and logic modeling.

28. The End